Processing sizes such as of a semiconductor device, a magnetic device, etc. have become minute and they are highly integrated, and deterioration of device characteristics and degradation of reliability have become important problems more than before. In recent years, in order to analyze failures of semiconductor devices in nanometer regions and ascertain causes of the failures fundamentally to solve them in processes of a development of a new process and mass production, there have become indispensable analysis means not only image observation by (scanning) transmission electron microscopy ((S)TEM) but also crystallography by electron diffraction, spectrum analysis and two-dimensional element distribution analysis both of which use electron energy loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDX), etc.
Moreover, in materials for energy conversion and environmental protection such as a positive electrode material of the lithium ion battery, rapid improvement in material characteristics more than before is desired. In order to improve the material characteristics, control of a structure in a nanometer level and a chemical bonding state hold important keys. Therefore, needs of the above-mentioned analysis technology are increasing.
Here, a measuring method for measuring an electron energy loss spectrum will be explained in detail out of the above-mentioned analysis means.
The electron energy loss spectra can be divided roughly into a zero loss spectrum that no energy is lost when passing through a sample, a plasmon loss spectrum obtained by exciting electrons in a valence band to lose energy, and an inner shell electron excitation loss spectrum obtained by exciting inner shell electrons to lose energy. In the inner shell electron excitation loss (core loss) spectrum, a fine structure is observed near an absorption edge.
This structure is called an absorption edge fine structure (Energy Loss Near-Edge Structure: ELNES), and has information reflecting an electronic state and a chemical bonding state of the sample. Moreover, since the energy loss value (an absorption edge position) is inherent to an element, qualitative analysis is possible. Moreover, since information relevant to coordination surrounding an attention element can also be acquired from a shift of the absorption edge position called a chemical shift, simple state analysis is also possible.
Conventionally, in the case of acquiring the electron energy loss spectra in different places on the sample, by combining a scanning transmission electron microscope that is made to scan a narrowly focused electron ray on the sample by a scanning coil and an electron spectrometer capable of conducting spectroscopy depending on an energy quantity that the electron ray has, electrons having penetrated the sample were subjected to spectroscopy and the electron energy loss spectrum was continuously acquired.
However, in the case of this technique, since aberration and an origin point of the electron energy loss spectrum vary by a drift of an acceleration voltage of the electron ray and variations of a magnetic field and an electric field that accompany a disturbance variation in a circumference of the apparatus, it is difficult to compare shapes of the absorption edge fine structures of the electron energy loss spectra and slight chemical shifts at measuring positions.
Then, for example, Patent Literature 1 describes that while a normal transmission electron microscope obtains a transmission electron microscope image such that focal positions of both the x-axis and the y-axis are set on the same plane, the above-mentioned transmission electron microscope includes an electron spectrometer and, by differentiating the focal positions of the x-axis and the y-axis, acquires a two-dimensional image such that the focal position of the x-axis is set on the spectrum plane and, on the other hand, the focal position of the y-axis is set on an image plane with the image detector.
As a result, the electron energy loss spectrum in a y-axis direction of the sample can be separated and observed. That is, an image obtained by an image detector can be observed as a spectral image whose x-axis represents an energy loss amount, i.e., is an energy dispersion axis, and whose y-axis has position information of the sample as shown in FIG. 2(b). The spectral image is observed in a belt-like shape corresponding to each layered film of the transmission electron microscope image shown in FIG. 2(a). Moreover, if the intensity profile of the spectral image is extracted in each place corresponding to each layered film from FIG. 2(a), it will be possible to simultaneously observe the electron energy loss spectra at different positions of the sample as show in FIG. 2A, which will make it possible to compare in detail the absorption edge fine structures of the electron energy loss spectra at different positions and slight chemical shifts.
A spectral image whose x axis has an energy loss amount and whose y-axis has position information of the sample that is described in the patent Literature 1 is a two-dimensional image obtained with an image detector by altering a lens action of the electron spectrometer, etc. and differentiating focal positions on the x-axis and the y-axis, that is, it is possible to simultaneously observe the electron energy loss spectra of multiple points at different positions of the sample. This technology discloses a technology by which the spectral images, i.e., the electron energy loss spectra are acquired from multiple different points in one sample, and the chemical shifts caused by differences in chemical bonding states are discussed.
Moreover, Patent Literature 2 discloses a sample holder for a transmission electron microscope by which spectral images can be acquired simultaneously from multiple samples, and electron energy loss spectra and chemical shifts can be measured.
The sample holder for a transmission electron microscope disclosed in Patent Literature 2 has a sample stage on which multiple sample stands can be arranged. Moreover, at least one sample stage can be moved by a moving mechanism, and multiple sample stands can be brought closer together.
The sample holder for a transmission electron microscope disclosed in the abovementioned Patent Literature 2 enables the Spectral images to be acquired from multiple samples simultaneously, which makes it possible to measure electron energy loss spectra and chemical shifts.
With the above-mentioned technology, it is possible to acquire the spectral images from the multiple samples simultaneously. However, in a holder of the above-mentioned technology, although an opening through which an electron ray passes is provided in a sample tip, an opening by which an ion beam is irradiated on the sample is not provided in a focused ion beam (FIB) apparatus used of preparation of a TEM sample, etc.; therefore, a thin sample for TEM cannot be prepared in the FIB using the holder of the above-mentioned technology. Therefore, after preparing a TEM sample by the FIB using another sample holder, it is necessary to reinstall it in the above-mentioned sample holder.
Patent Literature 3 discloses TEM sample preparation by the FIB and a sample holder that enables TEM observation.
With the above-mentioned disclosed technology, although sample preparation and TEM observation by the FIB is possible using the same sample holder, only one sample stand can be installed. Moreover, since the sample stand is unmovable, it is difficult to acquire EELS's simultaneously from the samples mounted on multiple sample stands.